Various types of fuel level sensors are used within fuel tanks to indicate a level of liquid fuel within the tank. One typical fuel level sensor includes a float attached to the end of a pivotable lever, which carries a wiper of a variable resistor. As the float and lever move in response to changes in liquid level, the wiper moves across a resistor card of the variable resistor to change the resistance of the variable resistor. Accordingly, the change in resistance effects a change in electrical signal output to a fuel gauge display. Another type of fuel level sensor may include a float connected to a sensor body by a rotatable lever attached at one end to the float and at an opposite end to a rotatable shaft. The rotatable shaft cooperates with an indicating means of the sensor body to effect a change in electrical signal output to a fuel gauge display.
With these types of fuel level sensors, the float generally floats on a surface of liquid fuel within a fuel tank and, thus, its vertical location within the tank corresponds to the level of liquid fuel. Accordingly, because the shaft, or wiper, is connected to the float via the pivotable lever, it assumes an angular position corresponding to the vertical location of the float. But it is necessary to calibrate the fuel level sensor to ensure precise correspondence between a sensed angular position of the shaft or wiper and the actual vertical location of the float. During calibration, the vertical location of the float and the angular position of the shaft or wiper are sensed at minimum and maximum levels.
From U.S. Pat. No. 5,485,740, it is known to measure the position of a float in an empty fuel tank and to store this float position in sensor electronics as a minimum level. Subsequently, the tank is completely filled with fuel, the float rises, and the resultant float position is stored in the sensor electronics as the maximum level. This calibration method, however, requires a significant amount of time to complete in waiting for the tank to fill.